As an actuator which utilizes a shape memory alloy, in the past there have been the actuators which are described in the Patent Literatures 1 to 3.
The Patent Literature 1 proposes a technique for designing a shape memory alloy actuator which has a two-way shape memory effect which enables the shape memory alloy actuator to withstand repeated operation a very large number of times, be strikingly lengthened in operating lifetime, be broadened in range of operation, and further be stabilized in shape. The “two-way shape memory effect” is the phenomenon whereby if deforming a shape memory alloy which memorizes a certain shape at a low temperature, then heating it, the alloy returns to its original memorized shape and, furthermore, if making it low in temperature, the alloy returns to the shape deformed to at the low temperature. With the two-way shape memory effect, by just heating and cooling, the shape memory alloy independently repeatedly changes in shape without requiring action of a bias force from the outside. In a shape memory alloy actuator which has a two-way shape memory effect, behavior storing two shapes—the shape deformed to at the time of a low temperature (shape in martensite state) and the shape returned to at the time of a high temperature (shape in matrix phase state)—is exhibited.
In a shape memory alloy actuator which is described in the Patent Literature 2, a plurality of shape memory alloy wires are arranged between a support member and a moving member—both flat plates in shape. These shape memory alloy wires are laid so as to contact mating parts formed at facing surfaces of the support member and moving member and, furthermore, so as to bridge them in a loose manner. The moving member is given external force from the outside to be pushed against the support member. The shape memory alloy wires are in a loose state at ordinary temperature. When electrified and heated, they contract to tense up and are extended straight whereby the moving member is moved.
In a drive device which is disclosed in the Patent Literature 3, there is provided an actuator which has a shape memory alloy wherein the speed of response is raised. In this actuator, the shape memory alloy is supplied with a drive current and made to generate heat to cause a return operation. Furthermore, control is performed to generate an amount of drive current for the shape memory alloy so as to give an amount of displacement of the shape memory alloy based on a target value of displacement of the moving member. The invention which is disclosed in the Patent Literature 3 is therefore a drive device which is constituted by an actuator which has a shape memory alloy which efficiently increases the speed of response of the actuator.